/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.nulldev.util.web.HttpServer3.util;

import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAdder;

/**
 * This is a stream that will only supply bytes up to a certain length - if its
 * position goes above that, it will stop.
 * <p>
 * This is useful to wrap ServletInputStreams. The ServletInputStream will block
 * if you try to read content from it that isn't there, because it doesn't know
 * whether the content hasn't arrived yet or whether the content has finished.
 * So, one of these, initialized with the Content-length sent in the
 * ServletInputStream's header, will stop it blocking, providing it's been sent
 * with a correct content length.
 * </p>
 *
 * @since 2.0
 */
public class BoundedInputStream extends InputStream {

	private static final int EOF = -1;

	/** the wrapped input stream */
	private final InputStream in;

	/** the max length to provide */
	private final long max;

	/** the number of bytes already returned */
	private final LongAdder pos = new LongAdder();

	/** the marked position */
	private final AtomicLong mark = new AtomicLong(EOF);

	/** flag if close should be propagated */
	private final AtomicBoolean propagateClose;

	/**
	 * Creates a new {@code BoundedInputStream} that wraps the given input stream
	 * and limits it to a certain size.
	 *
	 * @param in   The wrapped input stream
	 * @param size The maximum number of bytes to return
	 */
	public BoundedInputStream(final InputStream in, final long size) {
		this(in, size, true);
	}

	/**
	 * Creates a new {@code BoundedInputStream} that wraps the given input stream
	 * and limits it to a certain size.
	 *
	 * @param in   The wrapped input stream
	 * @param size The maximum number of bytes to return
	 */
	public BoundedInputStream(final InputStream in, final long size, final boolean allowClose) {
		// Some badly designed methods - eg the servlet API - overload length
		// such that "-1" means stream finished
		this.max = size;
		this.in = in;
		this.propagateClose = new AtomicBoolean(allowClose);
	}

	/**
	 * Creates a new {@code BoundedInputStream} that wraps the given input stream
	 * and is unlimited.
	 *
	 * @param in The wrapped input stream
	 */
	public BoundedInputStream(final InputStream in) {
		this(in, EOF);
	}

	/**
	 * Invokes the delegate's {@code read()} method if the current position is less
	 * than the limit.
	 * 
	 * @return the byte read or -1 if the end of stream or the limit has been
	 *         reached.
	 * @throws IOException if an I/O error occurs.
	 */
	@Override
	public int read() throws IOException {
		if (max >= 0 && pos.sum() >= max) {
			return EOF;
		}
		final int result = in.read();
		pos.increment();
		return result;
	}

	/**
	 * Invokes the delegate's {@code read(byte[])} method.
	 * 
	 * @param b the buffer to read the bytes into
	 * @return the number of bytes read or -1 if the end of stream or the limit has
	 *         been reached.
	 * @throws IOException if an I/O error occurs.
	 */
	@Override
	public int read(final byte[] b) throws IOException {
		return this.read(b, 0, b.length);
	}

	/**
	 * Invokes the delegate's {@code read(byte[], int, int)} method.
	 * 
	 * @param b   the buffer to read the bytes into
	 * @param off The start offset
	 * @param len The number of bytes to read
	 * @return the number of bytes read or -1 if the end of stream or the limit has
	 *         been reached.
	 * @throws IOException if an I/O error occurs.
	 */
	@Override
	public int read(final byte[] b, final int off, final int len) throws IOException {
		if (max >= 0 && pos.sum() >= max) {
			return EOF;
		}
		final long maxRead = max >= 0 ? Math.min(len, max - pos.sum()) : len;
		final int bytesRead = in.read(b, off, (int) maxRead);

		if (bytesRead == EOF) {
			return EOF;
		}

		pos.add(bytesRead);
		return bytesRead;
	}

	/**
	 * Invokes the delegate's {@code skip(long)} method.
	 * 
	 * @param n the number of bytes to skip
	 * @return the actual number of bytes skipped
	 * @throws IOException if an I/O error occurs.
	 */
	@Override
	public long skip(final long n) throws IOException {
		final long toSkip = max >= 0 ? Math.min(n, max - pos.sum()) : n;
		final long skippedBytes = in.skip(toSkip);
		pos.add(skippedBytes);
		return skippedBytes;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public int available() throws IOException {
		if (max >= 0 && pos.sum() >= max) {
			return 0;
		}
		return in.available();
	}

	/**
	 * Invokes the delegate's {@code toString()} method.
	 * 
	 * @return the delegate's {@code toString()}
	 */
	@Override
	public String toString() {
		return in.toString();
	}

	/**
	 * Invokes the delegate's {@code close()} method if {@link #isPropagateClose()}
	 * is {@code true}.
	 * 
	 * @throws IOException if an I/O error occurs.
	 */
	@Override
	public void close() throws IOException {
		if (propagateClose.get()) {
			in.close();
		}
	}

	/**
	 * Invokes the delegate's {@code reset()} method.
	 * 
	 * @throws IOException if an I/O error occurs.
	 */
	@Override
	public synchronized void reset() throws IOException {
		in.reset();
		pos.reset();
		pos.add(mark.get());
	}

	/**
	 * Invokes the delegate's {@code mark(int)} method.
	 * 
	 * @param readlimit read ahead limit
	 */
	@Override
	public synchronized void mark(final int readlimit) {
		in.mark(readlimit);
		mark.set(pos.sum());
	}

	/**
	 * Invokes the delegate's {@code markSupported()} method.
	 * 
	 * @return true if mark is supported, otherwise false
	 */
	@Override
	public boolean markSupported() {
		return in.markSupported();
	}

	/**
	 * Indicates whether the {@link #close()} method should propagate to the
	 * underling {@link InputStream}.
	 *
	 * @return {@code true} if calling {@link #close()} propagates to the
	 *         {@code close()} method of the underlying stream or {@code false} if
	 *         it does not.
	 */
	public boolean isPropagateClose() {
		return propagateClose.get();
	}

	/**
	 * Set whether the {@link #close()} method should propagate to the underling
	 * {@link InputStream}.
	 *
	 * @param propagateClose {@code true} if calling {@link #close()} propagates to
	 *                       the {@code close()} method of the underlying stream or
	 *                       {@code false} if it does not.
	 */
	public void setPropagateClose(final boolean propagateClose) {
		this.propagateClose.lazySet(propagateClose);
	}
}